In recent years there has been a tendency in the tobacco industry to produce tobacco products, particularly cigarettes, having filters with greater filtering efficiency and higher levels of dilution. This high filter efficiency and greater dilution reduces the total particulate matter or tar level of the cigarette and hence reduces the flavor to some extent.
Traditional, lit-end cigarettes comprise a cylindrical tobacco rod portion that is between 7.0 and 10.0 mm in diameter and 60 mm and 125 mm in length. The tobacco rod portion, which is composed of one or more selected types of cut tobacco, is wrapped in cigarette paper along its outer circumference. A filter, preferably of cellulose acetate or some other cellulosic material, is attached, in end-to-end relation, to the mouth end of the tobacco rod by a filter wrap. During puffs, smoke from the lit end of the cigarette travels the length of the tobacco rod and through the filter to the smoker.
U.S. Pat. No. 3,356,094 to Ellis et al., U.S. Pat. No. 4,340,072 to Bolt et al. and U.S. Pat. No. 4,732,168 to Resce et al. describe examples of smoking articles having a tobacco column with a tubular member therethrough, wherein the tube is filled with an aerosol releasing material. In these patents, smoke from the burning tobacco is mixed with the aerosol.
U.S. Pat. No. 4,924,886 to Litzinger discloses a smoking article having a central tube of an impermeable material located within a tobacco column, wherein the central tube contains a heat absorbing, porous non-tobacco substrate including a flavor releasing material. The flavor releasing material is mixed with the porous substrate and the flavor is volatile at the smoldering temperature of the tobacco in the tobacco column. An aerosol generating material also impregnates the porous substrate and becomes aerosolized by the heat generated by the smoldering tobacco.
In U.S. Pat. No. 4,984,588 to Stewart and U.S. Pat. No. 3,756,249 to Selke et al., a longitudinally extending tube is provided within the cigarette, surrounded by the tobacco filler material and an outer cigarette wrapper, with the longitudinally extending tube serving as an internal air passageway within the cigarette. In these known smoking articles, the central longitudinally extending tube is impermeable to air flow, and therefore serves to control the amount of dilution of the mainstream smoke depending on whether the impermeable tube is open to air flow or closed.
In U.S. Pat. No. 4,984,588 to Stewart, a smoking article is provided with a hollow, elongated tube of a combustible, heat fusible and air impermeable material that extends from approximately 5 mm from the mouth end of the filter to approximately 10 mm short of the end of the tobacco segment. As the cigarette is smoked, relatively undiluted smoke enters the tube during the initial several puffs and is delivered in a virtually unfiltered condition. After the first several puffs, the tube is melted shut and normal dilution occurs.
In view of the tendency for cigarettes to have greater filtering efficiency and higher levels of dilution, a cigarette structure that provides improved flavor delivery would be desirable. Furthermore, in the existing cigarettes provided with longitudinally extending tubes that remain open at an end to air flow through the tube, ambient air flows through the tube with very little resistance to the flow, and therefore any transfer of heat through the tube from the burning coal at the end of the cigarette would be negligible.